Room-temperature molten salt, process for producing the same and applications thereof

ABSTRACT

The present invention provides a room-temperature molten salt that is obtainable by mixing two or more organic salts and that has a solidifying point lower than the solidifying point (or melting point) of any of the starting organic salts, a process for producing the same, and use of the same. Specifically, the present invention provides a room-temperature molten salt that comprises a mixture of two or more organic salts with different anionic moieties and different organic cationic moieties and that has a melting point lower than any of the individual organic salts, a process for producing the same, and use of the same.

TECHNICAL FIELD

The present invention relates to a room-temperature molten saltobtainable by mixing two or more organic salts, a process for producingthe same, and use of the same.

BACKGROUND ART

Room-temperature molten salts have relatively high electricconductivity, a wide potential window and unique characteristics notpossessed by conventional electrolyte systems, i.e., nonflammability andnonvolatility. Thus, researchers have been studying the possibility ofusing room-temperature molten salts as battery electrolytes. Moreover,room-temperature molten salts have high polarity and can dissolve avariety of organic and inorganic compounds, and thereforeroom-temperature molten salts are being studied as environmentallyfriendly “green” solvents to be used in organic and inorganic reactions,catalytic reactions, biochemical reactions, liquid-liquid extraction andseparation, electrochemistry and other fields.

However, many room-temperature molten salts have a relatively highmelting point, and while are liquid at room temperature, are solidifiedwith a decrease in temperature. To expand their applications, organicsalts with a much lower melting point are demanded.

Generally, the synthesis process for a room-temperature molten saltcomprises two steps. As shown in the following reaction scheme, thefirst step is a quaternarization reaction, and the subsequent secondstep is anion exchange. For example, the process may comprise the stepsof reacting an imidazole derivative with an alkyl halide (R^(d)X) toform an imidazolium salt, and then exchanging its anion for an anion(Y⁻) that has an appropriate capability for forming a molten salt.

However, since room-temperature molten salts are liquid but nonvolatile,they cannot be distilled and have problems with purification. Forexample, in order to efficiently separate the salt (MX), which is aby-product in the process of the above reaction scheme, the followingmethods were proposed: a method using an expensive silver salt (J. Chem.Soc., Chem. Commun. (1992), 96); a method using the difference insolubilities (Japanese Unexamined Patent Publication No. 1996-259543);and methods comprising the step of neutralizing a tertiary amine with anorganic acid to give an onium salt by protonation (Electrochem. Acta,45, 1291 (2000); J. Electrochem. Soc., 147, 4168 (2000); Electrochem.Solid-State Lett., 4, E25 (2001); etc.). The methods using salt exchangeor solubility differences are disadvantageous in view of cost andefficiency. The method of synthesizing a protonated onium salt is easyand simple, but the protonated onium salt has lower performance thanalkylated onium salts.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a room-temperaturemolten salt that is obtainable by mixing two or more organic salts andthat has a solidifying point lower than the solidifying point (ormelting point) of any of the individual organic salts, a process forproducing the same, and use of the same.

The present inventors conducted extensive research to solve the aboveproblems and found that the above object can be achieved by mixing twoor more specific organic salts. By expanding this finding, the inventorsaccomplished the present invention.

The present invention provides the following items:

-   -   1. A room-temperature molten salt comprising a mixture of two or        more organic salts with different anionic moieties and different        organic cationic moieties, the room-temperature molten salt        having a solidifying point lower than that of any of the        individual organic salts.    -   2. A room-temperature molten salt according to item 1, wherein        the two or more organic salts are selected from the group        consisting of the organic salts represented by formulae (I),        (II), (III) and (IV):        wherein R^(1a) to R^(5a), R^(7a), R^(9a) and R^(10a) are the        same or different and each represents a hydrogen atom, a halogen        atom, an alkyl group, a cycloalkyl group, a heterocyclic group,        a haloalkyl group, an aralkyl group, an aryl group, an alkoxy        group, an aryloxy group or an aralkyloxy group; R^(8a) is a        hydrogen atom, an alkyl group, a cycloalkyl group, a        heterocyclic group, a haloalkyl group, an aralkyl group or an        aryl group; R^(6a), R^(11a), R¹², R¹³, R¹⁴, R¹⁵, R¹⁶, R¹⁷, R¹⁸        and R¹⁹ are the same or different and each represents an alkyl        group, a cycloalkyl group, a heterocyclic group, a haloalkyl        group, an aralkyl group or an aryl group; two groups selected        from R¹², R¹³, R¹⁴ and R¹⁵ may be linked at their ends to form,        together with the adjacent nitrogen atom, a nitrogen-containing        aliphatic heterocycle; two groups selected from R¹⁶, R¹⁷, R¹⁸        and R¹⁹ may be linked at their ends to form, together with the        adjacent phosphorus atom, a phosphorus-containing aliphatic        heterocycle; and X₁ ⁻, X₂ ⁻, X₃ ⁻ and X₄ ⁻ are each a conjugate        base of a Brönsted acid.    -   3. A room-temperature molten salt according to item 1 or 2,        wherein at least one of the two or more organic salts is a solid        at room temperature.    -   4. A room-temperature molten salt according to item 1 or 2,        wherein all of the two or more organic salts are solids at room        temperature.    -   5. A room-temperature molten salt according to item 1 or 2,        wherein at least one of the two or more organic salts is        selected from the group consisting of the organic salts        represented by formulae (V) and (VI):        wherein R¹ to R⁵, R⁷, R⁹ and R¹⁰ are the same or different and        each represents a hydrogen atom, a halogen atom, an alkyl group,        a cycloalkyl group, a heterocyclic group, a haloalkyl group, an        aralkyl group, an aryl group, an alkoxy group, an aryloxy group        or an aralkyloxy group; R⁸ is a hydrogen atom, an alkyl group, a        cycloalkyl group, a heterocyclic group, a haloalkyl group, an        aralkyl group or an aryl group; R⁶ and R¹¹ are the same or        different and each represents a C₁₋₁₀ alkyl group in which at        least one hydrogen atom is substituted by fluorine; and X₁ ⁻ and        X₂ ⁻ are each a conjugate base of a Brönsted acid.    -   6. A room-temperature molten salt according to item 5, wherein        all of the two or more organic salts are selected from the group        consisting of the organic salts represented by formulae (V) and        (VI).    -   7. A room-temperature molten salt according to item 5 or 6,        wherein at least one of the two or more organic salts is a solid        at room temperature.    -   8. A room-temperature molten salt according to item 5 or 6,        wherein all of the two or more organic salts are solids at room        temperature.    -   9. A room-temperature molten salt according to any one of items        5 to 8, wherein, in formulae (V) and (VI), R¹ to R⁵, R⁷, R⁹ and        R¹⁰ are the same or different and each represents a hydrogen        atom, a halogen atom, an alkyl group or a haloalkyl group; R⁸ is        an alkyl group; R⁶ and R¹¹ are the same or different and each        represents a group of the formula —CH₂R¹² wherein R¹² is a        straight- or branched-chain C₁₋₉ alkyl group in which at least        one hydrogen atom is substituted by fluorine.    -   10. A room-temperature molten salt according to item 6, wherein        all of the two or more organic salts are selected from the group        consisting of the organic salts represented by formula (V) and        are solids at room temperature.    -   11. A room-temperature molten salt according to item 6, wherein        all of the two or more organic salts are selected from the group        consisting of the organic salts represented by formula (VI) and        are solids at room temperature.    -   12. A room-temperature molten salt according to item 6, wherein        the two or more organic salts are at least one organic salt that        is selected from the group consisting of the organic salts        represented by formula (V) and is a solid at room temperature,        and at least one organic salt that is selected from the group        consisting of the organic salts represented by formula (VI) and        is solid at room temperature.    -   13. A room-temperature molten salt according to item 6, wherein        the two or more organic salts are two organic salts that are        selected from the group consisting of the organic salts        represented by formulae (V) and (VI) and that are solids at room        temperature; one of the organic salts having an anionic moiety        represented by the formula        (RfSO₂)₂N⁻ or (RfSO₂)(Rf′SO₂)N⁻        wherein Rf and Rf′ are different and each represents a        polyfluoroalkyl group; and        the other of the organic salts having an anionic moiety        represented by the formula        Rf″SO₃ ⁻        wherein Rf″ is a polyfluoroalkyl group.    -   14. A room-temperature molten salt obtainable by mixing two or        more organic salts with different anionic moieties and different        organic cationic moieties, the room-temperature molten salt        having a solidifying point lower than that of any of the        individual organic salts.    -   15. A process for producing a room-temperature molten salt,        comprising mixing two or more organic salts with different        anionic moieties and different organic cationic moieties, the        room-temperature molten salt having a solidifying point lower        than that of any of the individual organic salts.    -   16. A process according to item 15, wherein the two or more        organic salts are selected from the group consisting of the        organic salts represented by formulae (I) to (IV).    -   17. A process according to item 15 or 16, wherein at least one        of the two or more organic salts is a solid at room temperature.    -   18. A process according to item 15 or 16, wherein all of the two        or more organic salts are solids at room temperature.    -   19. A process according to item 15, wherein the two or more        organic salts are selected from the group consisting of the        organic salts represented by formulae (V) and (VI) and are        solids at room temperature.    -   20. An electrolytic solution comprising a room-temperature        molten salt according to any one of items 1 to 14.    -   21. A battery comprising an electrolytic solution according to        item 20, a positive electrode, a negative electrode and a        separator.    -   22. A battery according to item 21, which is a nonaqueous        lithium secondary battery.    -   23. A solvent for use in organic reaction solvent comprising a        room-temperature molten salt according to any one of items 1 to        14.    -   24. An extraction solvent comprising a room-temperature molten        salt according to any one of items 1 to 14.    -   25. A capacitor comprising an electrolyte or electrolytic        solution that comprises a room-temperature molten salt according        to any one of items 1 to 14.    -   26. An electric double layer capacitor comprising an electrolyte        or electrolytic solution that comprises a room-temperature        molten salt according to any one of items 1 to 14.    -   27. A dye-sensitized solar cell comprising a room-temperature        molten salt according to any one of items 1 to 14.    -   28. A fuel cell comprising a room-temperature molten salt        according to any one of items 1 to 14.    -   29. A polymer electrolyte fuel cell comprising a        room-temperature molten salt according to any one of items 1 to        14.

The present invention is described below in detail.

Room-temperature Molten Salt of the Present Invention

With respect to the room-temperature molten salt of the presentinvention, “room temperature” is in the range of from about 20° C. toabout 30° C. In the present invention, an “organic salt that is a solidat room temperature” means an organic salt that is in a solid state inthe temperature range of about 20° C. to about 30° C., and“room-temperature molten salt” means an organic salt that is in a liquidstate in the temperature range of about 20° C. to about 30° C. Theabove-mentioned temperatures are all at atmospheric pressure.

The room-temperature molten salt of the present invention is produced bymixing two or more organic salts that are different from each other bothin anionic moiety and cationic moiety. The room-temperature molten saltexhibits a much lower solidifying point than the solidifying points (ormelting points) of the individual starting organic salts, and isobtained as a mixed organic salt that is liquid at room temperature.Namely, the room-temperature molten salt is characterized in that thesalt is produced by mixing two or more organic salts with differentanionic moieties and different cationic moieties, and thereby has a muchlowered solidifying point than the individual organic salts.

As used herein, “anionic moiety” means a negatively charged componentthat constitutes a part of the each organic salt, and “cationic moiety”means a positively charged component that constitutes a part of eachorganic salt. As mentioned hereinafter, cationic moieties are organic.

Specifically, the room-temperature molten salt of the present inventioncan be obtained by mixing two or more organic salts selected from thegroup consisting of the organic salts represented by formulae (I), (II),(III) and (IV). In particular, to obtain the room-temperature moltensalt of the present invention in high purity, it is preferable that atleast one of the two or more starting organic salts is a solid at roomtemperature, and more preferably, all of the individual organic saltsare solids at room temperature.

It is preferable that at least one, and more preferably all of the twoor more starting organic salts are selected from the group consisting ofthe organic salts represented by formulae (V) and (VI). Also in thiscase, at least one of the two or more organic salts is preferably asolid at room temperature, and more preferably all of the organic saltsare solids at room temperature.

Further, the room-temperature molten salt of the present invention canbe obtained by mixing two or more organic salts selected from the groupconsisting of the organic salts represented by formula (V). Of the twoor more starting organic salts, preferably at least one, and morepreferably all are solids at room temperature.

Furthermore, the room-temperature molten salt of the present inventioncan be obtained by mixing two or more organic salts selected from thegroup consisting of the organic salts represented by formula (VI). Ofthe two or more starting organic salts, preferably at least one, andmore preferably all are solids at room temperature.

Moreover, the room-temperature molten salt of the present invention canbe obtained by mixing at least one organic salt that is selected fromthe group consisting of the organic salts represented by formula (V) andis a solid at room temperature, and at least one organic salt that isselected from the group consisting of the organic salts represented byformula (VI) and is a solid at room temperature.

The substituents in formulae (I) to (IV) are as defined above, andexamples thereof are as follows. (i) R^(1a) to R^(5a), R^(7a), R^(9a)and R^(10a) Examples of halogen atoms include fluorine, chlorine,bromine and iodine atoms.

Examples of alkyl groups include straight- or branched-chain C₁₋₁₀ alkylgroups, and preferable are straight- or branched-chain C₁₋₆ alkyl groupssuch as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,sec-butyl, tert-butyl, n-pentyl, n-hexyl, neopentyl, isohexyl, etc.

Examples of cycloalkyl groups include C₃₋₁₀ cycloalkyl groups, andpreferable are C₃₋₆ cycloalkyl groups such as cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, etc.

Examples of heterocyclic groups include three- to six-membered aliphaticand aromatic mono-heterocyclic groups with at least one hetero atomselected from the group consisting of nitrogen atoms, oxygen atoms andsulfur atoms. Specific examples include aziridinyl, pyrrolidinyl,piperidyl, piperazinyl, morpholinyl, tetrahydropyranyl, pyridyl, furyl,thienyl, etc. Substituent(s) may be bonded to such heterocyclic groups.Examples of substituents include fluorine, chlorine and like halogenatoms; methyl, ethyl and like alkyl groups; trifluoromethyl and likehaloalkyl groups; methoxy, ethoxy and like alkoxy groups; phenyl andlike aryl groups; etc.

Examples of haloalkyl groups include alkyl groups in which at least onehydrogen atom is substituted by halogen, and preferable are straight- orbranched-chain C₁₋₁₀ alkyl groups in which at least one hydrogen atom issubstituted by fluorine. Specific examples include trifluoromethyl,trifluoroethyl, trichloroethyl, tetrafluoroethyl, perfluoroethyl,perfluoropropyl, perfluoroisopropyl, perfluorobutyl, perfluorohexyl,perfluorooctyl, perfluorodecyl, 2-(perfluorooctyl)ethyl,1H,1H,3H-tetrafluoropropyl, 1H,1H,5H-octafluoropentyl, etc. Among these,especially preferable are C₁₋₆ straight- or branched-chain alkyl groupsin which at least one hydrogen atom is substituted by fluorine, such astrifluoromethyl, trifluoroethyl, trichloroethyl, tetrafluoroethyl,perfluoroethyl, perfluoropropyl, perfluoroisopropyl, perfluorobutyl,perfluorohexyl, etc.

Examples of aralkyl groups include C₇₋₁₀ aralkyl groups. Specificexamples include 2-phenylethyl, benzyl, 1-phenylethyl, 3-phenylpropyl,4-phenylbutyl, etc.

Examples of aryl groups include phenyl groups, naphthyl groups, etc.Substituent(s) may be bonded to such aryl groups. Examples ofsubstituents include fluorine, chlorine and like halogen atoms; methyl,ethyl and like alkyl groups; trifluoromethyl and like haloalkyl groups;methoxy, ethoxy and like alkoxy groups; phenyl and like aryl groups;etc.

Examples of alkoxy groups include straight- or branched-chain C₁₋₁₀alkoxy groups, and preferable are straight- or branched-chain C₁₋₆alkoxy groups such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy,isobutoxy, sec-butoxy, tert-butoxy, pentyloxy, hexyloxy, etc.

Examples of aryloxy groups include phenoxy, naphthyloxy and like groups.

Examples of aralkyloxy groups include C₇₋₁₀ aralkyloxy groups, andspecific examples include 2-phenylethyloxy, benzyloxy, 1-phenylethyloxy,3-phenylpropyloxy, 4-phenylbutyloxy, etc.

(ii) R^(8a)

Examples of alkyl, cycloalkyl, heterocyclic, haloalkyl, aralkyl and arylgroups are as described above.

(iii) R^(6a), R^(11a), R¹², R¹³, R¹⁴, R¹⁵, R¹⁶, R¹⁷, R¹⁸ and R¹⁹

Examples of alkyl, cycloalkyl, heterocyclic, haloalkyl, aralkyl and arylgroups are as described above.

When R^(6a) and R^(11a) are haloalkyl groups, C₁₋₁₀ alkyl groups inwhich at least one hydrogen atom is substituted by fluorine arepreferable. Examples of such haloalkyl groups include straight- orbranched-chain C₁₋₁₀ perfluoroalkyl groups, straight- or branched-chainC₁₋₁₀ polyfluoroalkyl groups, etc. Specific examples of straight- orbranched-chain C₁₋₁₀ perfluoroalkyl groups include perfluoroethyl,perfluoropropyl, perfluorobutyl, perfluoropentyl, perfluorohexyl,perfluoroheptyl, perfluorooctyl, perfluorononyl, perfluorodecyl, etc.Examples of straight- or branched-chain C₁₋₁₀ polyfluoroalkyl groupsinclude the above-mentioned alkyl groups in which at least one hydrogenatom is substituted by fluorine. Specific examples of suchpolyfluoroalkyl groups include CF₃CH₂, CF₃CF₂CH₂, CF₃CF₂CF₂CH₂,CF₃CF₂(CH₂)₆, HCF₂CF₂CH₂, HCF₂CF₂CF₂CF₂CH₂, H(CF₂)₆CH₂, CF₃CHFCF₂CH₂,(CF₃)₂CH, (CF₃)₂CHCH₂, (CF₃)₂C(CH₃)CH₂, etc.

Particularly preferable examples of R⁶ and R¹¹ include groupsrepresented by the formula —CH₂R¹² wherein R¹² is a straight- orbranched-chain C₁₋₉ alkyl group in which at least one hydrogen atom issubstituted by fluorine. Preferable examples of R¹² include straight- orbranched-chain C₁₋₆ alkyl groups in which at least one hydrogen atom issubstituted by fluorine, such as fluoromethyl, difluoromethyl,trifluoromethyl, perfluoroethyl, perfluoropropyl, CF₃CF₂(CH₂)₅, HCF₂CF₂,H(CF₂)₄, H(CF₂)₆, (CF₃)₂CH, CF₃CHFCF₂, etc.

When two groups selected from R¹², R¹³, R¹⁴ and R¹⁵ are linked at theirends to form, together with the adjacent nitrogen atom, anitrogen-containing aliphatic heterocycle, examples of thenitrogen-containing aliphatic heterocycles include three- toten-membered nitrogen-containing aliphatic heterocycles, and specificexamples include aziridine, pyrrolidine, piperidine, morpholine,perhydro-2H-azepine, etc.

When two groups selected from R¹⁶, R¹⁷, R¹⁸ and R¹⁹ are linked at theirends to form, together with the adjacent phosphorus atom, aphosphorus-containing aliphatic heterocycle, the phosphorus-containingaliphatic heterocycle may be, for example, a three- to ten-memberedphosphorus-containing aliphatic heterocycle. Specific examples includephosphirane, phosphetane, phosphol, etc.

(vi) X₁ ⁻, X₂ ⁻, X₃ ⁻ and X₄ ⁻

X₁ ⁻, X₂ ⁻, X₃ ⁻ and X₄ ⁻ each represent an anionic moiety of theindividual starting organic salts. The anionic moiety is a conjugatebase of a Brönsted acid. Examples of such Brönsted acids includeBrönsted acids with strong acidity, such as sulfuric acid; monomethylsulfate, monoethyl sulfate and like sulfuric acid monoesters;methansulfonic acid, ethanesulfonic acid, chlorosulfonic acid,fluorosulfonic acid, benzenesulfonic acid, toluenesulfonic acid,nitrobenzenesulfonic acid, trichloromethanesulfonic acid, acidsrepresented by the formula Rf″SO₃H wherein Rf″ is a polyfluoroalkylgroup, and like sulfonic acids; sulfonimides represented by the formula(RfSO₂)₂NH or (RfSO₂)(Rf′SO₂)NH wherein Rf and Rf′ are different andeach represents a polyfluoroalkyl group; formic acid, acetic acid,butyric acid, valeric acid, trifluoroacetic acid, perfluorobutyric acid,perfluorooctanoic acid, 3H-octafluorobutyric acid, trichloroacetic acidand like carboxylic acids; HB(OCOCF₃)₄, HB(OCOC₂F₅)₄, HBPh₄, HB(C₆F₅)₄,HB(p-CF₃C₆H₄)₄, HB[3,5-(CF₃)₂C₆H₃], HC(SO₂CF₃)₃, HC(SO₂C₂F₅)₃ and likeorganic acids; HBF₄, HPF₆, HSbF₆, HAsF₆, HBCl₄, HBCl₃F, HSbCl₆, HSbCl₅F,HClO₄, HNO₃, HAlCl₄, HAl₂Cl₇ and like inorganic acids; etc.

The polyfluoroalkyl groups represented by Rf, Rf′ and Rf″ may be thesame or different and may be independently a straight- or branched-chainC₁₋₆ perfluoroalkyl group or a straight- or branched-chain C₁₋₆ alkylgroup in which at least one hydrogen atom is substituted by fluorine.Specific examples include trifluoromethyl, pentafluoroethyl,trifluoroethyl, perfluoropropyl, perfluorobutyl, etc.

Examples of acids represented by the formula Rf″SO₃H include C₄F₉SO₃H,CF₃SO₃H, CF₃CF₂SO₃H, CF₃CH₂SO₃H, HCF₂CF₂CH₂SO₃H, C₆Fl₃SO₃H,HCF₂CF₂CF₂CF₂SO₃H, etc.

Examples of sulfonimides include (CF₃SO₂)₂NH, (C₂F₅SO₂)₂NH,(C₄F₉SO₂)₂NH, (CF₃SO₂)(C₄F₉SO₂)NH, (C₂F₅SO₂)(C₄F₉SO₂)NH,(HCF₂CF₂SO₂)₂NH, (CF₃CH₂SO₂)(C₄F₉SO₂)NH, etc.

As mentioned above, the organic salts for use as the starting materialsof the room-temperature molten salt of the present invention all havedifferent anionic moieties (conjugate bases of Brönsted acids).

Preferable organic salts for use as starting materials include organicsalts of formulae (V) and (VI) wherein R¹ to R⁵, R⁷, R⁹ and R¹⁰ are thesame or different and each represents a hydrogen atom, a halogen atom,an alkyl group or a haloalkyl group; R⁸ is an alkyl group; R⁶ and R¹¹are the same or different and each represents a group represented by theformula —CH₂R¹² wherein R¹² is a straight- or branched-chain C₁₋₉ alkylgroup in which at least one hydrogen atom is substituted by fluorine.

With respect to the substituents of the organic salts of formulae (V)and (VI), examples of R¹ to R⁵, R⁷, R⁸ and R⁹ and R¹⁰ are the same asthose of R^(1a) to R^(5a), R^(7a), R^(8a), R^(9a) and R^(10a),respectively.

In R⁶ and R¹¹ represented by the formula —CH₂R¹² wherein R¹² is astraight- or branched-chain C₁₋₉ alkyl group in which at least onehydrogen atom is substituted by fluorine, preferable examples of R¹²include fluoromethyl, difluoromethyl, trifluoromethyl, perfluoroethyl,perfluoropropyl, CF₃CF₂(CH₂)₅, HCF₂CF₂, H(CF₂)₄, H(CF₂)₆, (CF₃)₂CH,CF₃CHFCF₂ and like straight- or branched-chain C₁₋₆ alkyl groups inwhich at least one hydrogen atom is substituted by fluorine.

Preferably, the room-temperature molten salt of the present invention isobtained by mixing two or more organic salts that are selected from thegroup consisting of the organic salts represented by formulae (V) and(VI) and are solid at room temperature. It is particularly preferable toobtain the room-temperature molten salt by mixing two organic salts thatare selected from the group consisting of the organic salts representedby formulae (V) and (VI) and are solid at room temperature. Preferableexamples of the two organic salts include the combination of an organicsalt with an anionic moiety represented by the formula(RfSO₂)₂N⁻ or (RfSO₂)(Rf′SO₂)N⁻wherein Rf and Rf′ are different and each represents a polyfluoroalkylgroup, and an organic salt with an anionic moiety represented by theformulaRf″ SO₃ ⁻wherein Rf″ is a polyfluoroalkyl group.

Of the room-temperature molten salts according to the present invention,preferable are those obtained by mixing organic salts selected from thefollowing <organic salts>, and those obtained by mixing two or moreorganic salts selected from the following <organic salts>. Inparticular, room-temperature molten salts obtained by mixing two orthree organic salts selected from the following <organic salts> arepreferable. The following <organic salts> are preferably solids at roomtemperature. “Tf⁻” in the organic salts means a trifluoromethanesulfonylgroup (CF₃SO₂—).

Process for Producing the Room-temperature Molten Salt of the PresentInvention

The starting organic salts of formulae (I) to (VI) for theroom-temperature molten salt of the present invention can be synthesizedby, for example, the processes described in Inorg. Chem. (1996) 35,1168, and Bull. Chem. Soc. Jpn., (1991) 64, 2008.

The room-temperature molten salt of the present invention is produced bymixing two or more organic salts with different anionic moieties anddifferent organic cationic moieties. In the production process, themixing ratio of the two or more organic salts selected from the groupconsisting of the organic salts represented by formulae (I) to (VI) isnot limited, and is suitably selected so that the organic salts can bemixed to form a uniform liquid. A suitable mixing ratio is, for example,100 parts by weight of one of the organic salts and about 1 to about1000 parts by weight, preferably about 10 to about 500 parts by weight,and more preferably about 30 to about 300 parts by weight of each of theother organic salts. In order to obtain a room-temperature molten saltwith a low solidifying point, it is preferable to mix approximatelyequal weights of the two or more organic salts.

The solidifying point of the room-temperature molten salt of the presentinvention varies with the types and mixing ratio of the starting organicsalts, and is usually about 10° C. lower, preferably about 20° C. lower,more preferably about 50° C. lower, and particularly preferably 80° C.lower, than the organic salt with the lowest solidifying point of allthe starting organic salts used. For example, when the room-temperaturemolten salt is produced by mixing approximately equal weights of twoorganic salts that are selected from the group consisting of the organicsalts represented by formulae (V) and (VI) and are solids at roomtemperature, the room-temperature molten salt may have a solidifyingpoint about 50° C. to about 100° C. lower than that of the organic saltwith the lowest solidifying point. In particular, when organic saltsselected from the above <organic salts> are mixed, the resultingroom-temperature molten salt of the present invention has a greatlylowered solidifying point than any of the individual starting organicsalts.

The method of mixing the organic salts is not limited, and may be aknown method, for example, mixing in a mortar, mixing with a stirrer, ormixing with heating. When using the room-temperature molten salt of thepresent invention as a nonaqueous battery electrolyte or the like, it ispreferable to mix the organic salts in a dry atmosphere to preventmoisture from being admixed.

In particular, when the starting organic salts are solids around roomtemperature, purification is very easy since organic and inorganicimpurities can be removed by a simple process, such as washing,recrystallization or the like. Thus, use of starting organic salts thatare solid at room temperature makes it possible to obtain theroom-temperature molten salt of the present invention in high purity.Accordingly, to obtain the room-temperature molten salt of the presentinvention in high purity, it is preferable that at least one of thestarting organic salts is a solid at room temperature, and morepreferably all of the starting organic salts are solids at roomtemperature.

The room-temperature molten salt of the present invention thus obtainedhas almost no vapor pressure, has high heat resistance, is liquid over awide temperature range because of its low solidifying point, and has ahigh ionic conductivity. Moreover, especially when containing fluorinein the molecule, the room-temperature molten salt has the features ofhigh flame retardancy and low viscosity.

Since the room-temperature molten salt of the present invention is amixture, it sometimes does not exhibit a clear solidifying point.Therefore, in this specification and the appended claims, “solidifyingpoint” of the room-temperature molten salt of the present invention isintended to mean the value measured by the method described inExperiment 1. Specifically, the room-temperature molten salt of thepresent invention is placed in an inert gas (e.g., argon) atmosphere inan airtight container and cooled at a rate of 2 to 3° C./min, and thetemperature at which the beginning of precipitation of theroom-temperature molten salt as a solid is observed with the naked eyeis determined as the “solidifying point”.

The “solidifying point” of the room-temperature molten salt as definedabove can be measured with good reproducibility by the method ofExperiment 1, but supercooling may occur before the precipitation ofsolids. Therefore, in addition to the above solidifying pointmeasurement, the precipitation temperature (glass transitiontemperature) of an amorphous solid of the room-temperature molten saltwas measured using a differential scanning calorimeter (DSC).

These measurements reveal that some of the room-temperature molten saltsaccording to the present invention have the feature of not having amelting point and not undergoing a phase change (primary phase change)in a temperature range from room temperature to extremely lowtemperatures. For example, this feature is noticeable in preferableroom-temperature molten salts of the invention obtained by mixing two ormore organic salts that are selected from the group consisting of theorganic salts represented by formulae (V) and (VI) and are solids atroom temperature.

Specifically, as shown in Experiment 2, differential scanningcalorimeter (DSC) measurements were performed on room-temperature moltensalts according to the present invention (Examples 1, 3 and 4) and1-ethyl-3-methylimidazolium trifluoromethanesulfonate, i.e., a knownroom temperature-molten salt (Comparative Example 5). Theroom-temperature molten salt of Comparative Example 5 was observed tohave a melting point (Tm) around −13° C., while in respect of theroom-temperature molten salts of Examples 1, 3 and 4, no melting point(Tm) was observed and only a glass transition temperature (Tg) wasobserved around −50° C. These results demonstrate that theroom-temperature molten salts of the present invention obtained inExamples 1, 3 and 4 undergo no phase change until they reach the glasstransition temperature around −50° C. Thus, salts that initially have amelting point can be easily converted, by being mixed, to aroom-temperature molten salt that has no melting point and does notundergo a phase change until it reaches the glass transitiontemperature.

Use of the Room-temperature Molten Salt of the Present Invention

Because of the above features, the room-temperature molten salt of thepresent invention can be used, singly or in combination with a solventheretofore used in electrolytic solutions, as an electrolyte orelectrolytic solution for lithium ion (primary or secondary) batteries.Examples of solvents heretofore used in electrolytic solutions includeknown nonaqueous organic solvents such as propylene carbonate, ethylenecarbonate, diethyl carbonate, dimethyl carbonate, methyl ethylcarbonate, dimethoxyethane, γ-butyrolactone, methyl acetate, methylformate, etc. The room-temperature molten salt of the present inventioncan be added as an electrolyte or a part of an electrolytic solution tothese solvents to form an electrolytic solution. The electrolyticsolution comprising the room-temperature molten salt of the presentinvention may further contain LiPF₆, LiPF₄(CF₃)₂, LiPF₄(C₂F₅)₂,LiPF₄(C₃F₇)₂, LiAsF₆, LiBF₄, LiClO₄, LiCF₃SO₃, LiC₄F₉SO₃, LiN(CF₃SO₂)₂,LiN(C₂F₅SO₂)₂, LiN(C₄F₉SO₂)₂, LiN(CF₃SO₂)(C₄F₉SO₂), LiC(CF₃SO₂)₃ and/orlike lithium salts as an electrolyte. The concentration of the lithiumsalt electrolyte(s) is not limited, and a concentration of 0.5 mol/l to1.5 mol/l is usually practical. Of course, it is preferable that theelectrolytic solution have a water content not greater than 10 ppm.

The above electrolyte and the room-temperature molten salt of thepresent invention can be used as an electrolyte for nonaqueous solutionswith lithium ion conductivity, or for a gel electrolyte comprising theelectrolyte immobilized in a polymer matrix, as described in, forexample, J. Electrochem. Soc., (2000) 147, 34.

Especially when the room-temperature molten salt of the presentinvention is produced by mixing organic salts that are solids at roomtemperature, the starting organic salts can be purified byrecrystallization or like processes, and as a result of thepurification, the obtained room-temperature molten salt is free ofinorganic salt impurities. Therefore, such a room-temperature moltensalt is especially preferable for use as lithium ion (primary orsecondary) battery electrolytes or electrolytic solutions which arerequired to have high purity.

Moreover, as mentioned above, the room-temperature molten salt of thepresent invention is liquid over a wide temperature range, and thus thelithium ion battery of the present invention, which comprises theroom-temperature molten salt as an electrolyte or a part of anelectrolytic solution, has the feature of exhibiting stable batterycharacteristics in environments with a wide temperature range (e.g., incold districts).

In producing a lithium ion (primary or secondary) battery, knownpositive and negative electrodes, separators and the like can be used assuch.

The battery may have the shape of, for example, a cylinder, square,button, film or the like.

Examples of negative electrode materials include lithium metals andalloys thereof, carbon or polymer materials capable of being doped anddedoped with lithium, lithium-intercalated compounds such as metaloxides, etc.

Examples of positive electrode materials include complex oxides oflithium and a transition metal, such as LiCoO₂, LiNiO₂, LiMn₂O₄ andLiMnO₂, polymer materials, etc.

Usable separators include, for example, porous membranes of polymermaterials such as polyethylene and polypropylene, polymer materialscapable of immobilizing the electrolytic solution of the presentinvention (so-called gel electrolyte), etc.

Examples of collector materials include copper, aluminum, stainlesssteel, titanium, nickel, tungsten steel, carbon materials, etc. Thecollector may be in the form of, for example, a foil, net, nonwovenfabric, punched metal or the like.

The room-temperature molten salt of the present invention can be used asa solvent in various organic synthesis reactions. The room-temperaturemolten salt has low solubility in water, and in particular, when theanionic moiety of the organic salts forming the room-temperature moltensalt is Rf″SO₃ ⁻, (RfSO₂)₂N⁻ or (RfSO₂)(Rf′SO₂)N⁻ wherein Rf, Rf′ andRf″ are as defined above, Ph₄B⁻, (C₆H₅)₄B⁻, (p-CF₃C₆H₄)₄B⁻,[3,5-(CF₃)₂C₆H₃]₄B⁻ or the like, the room-temperature molten salt hasextremely low solubility in water. Such a room-temperature molten saltmakes it possible to construct a two-phase reaction system consisting ofwater and the room-temperature molten salt. Moreover, since theroom-temperature molten salt is sparingly soluble in low-polarityorganic solvents (e.g., toluene, ethyl acetate, diethyl ether, etc.), itis also possible to construct a three-phase reaction system consistingof an organic solvent, water and the room-temperature molten salt.Further, the room-temperature molten salt has high heat resistance andtherefore enables the selection of reaction conditions from a widetemperature range. Furthermore, the room-temperature molten salt, afterbeing used as a reaction solvent, can be used as an extraction solventfor separation and purification as described below.

The room-temperature molten salt of the present invention can also beused as an extraction solvent for separation and purification in organicsynthesis reactions. For example, in a post-treatment of a reactionmixture containing a catalyst (e.g., a metal catalyst), when thereaction solvent is distilled off and then an ether and theroom-temperature molten salt of the present invention are added to theresidue, a two-phase system is formed in which the reaction product andcatalyst are held in the ethereal phase and room-temperature molten saltphase, respectively. Therefore, the reaction product can be easilyseparated from the catalyst and purified. Moreover, in some types ofreactions, the catalyst held in the room-temperature molten salt retainsits activity and can be recycled. Thus, the room-temperature molten saltof the present invention is extremely useful as an environmentallyfriendly solvent (see Chemistry, vol. 56, No.5 (2001)).

Furthermore, the room-temperature molten salt of the present inventionhas high heat resistance, is liquid over a wide temperature range andhas high ion conductivity as mentioned above, and therefore can also beused as an electrolytic solution for plating.

The room-temperature molten salt of the present invention does notundergo a phase change until it reaches an extremely low temperature,and has excellent low temperature properties. Because of thesecharacteristics, the room-temperature molten salt is usable, besides inthe above applications, as an electrolyte and/or electrolytic solutionfor fuel cells (in particular polymer electrolyte fuel cells),dye-sensitized solar cells, biological batteries or capacitors (inparticular electric double layer capacitors); an electro-rheologicalfluid; a heat storage medium; a catalyst; etc.

BRIEF EXPLANATION OF THE DRAWINGS

FIGS. 1 to 4 are graphs indicating the results of the differentialscanning calorimeter (DSC) measurements of the room-temperature moltensalts of Examples 1, 3 and 4 and Comparative Example 5, respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

The following Examples illustrate the present invention in furtherdetail, but are not intended to limit the scope thereof.

A. Synthesis of Starting Organic Salts

REFERENCE EXAMPLE 1

Synthesis of 1-(2,2,2-trifluoroethyl)-3-methylpyridiniumtrifluoromethanesulfonate

3-methylpyridine (5 mmol, 487 FL) and 2,2,2-trifluoroethyltrifluoromethanesulfonate (5 mmol, 1.16 g) in 1,1,1-trichloroethane (2mL) were heated and refluxed for 1.5 hours. The layered reaction mixturewas separated, and the reaction product was washed with1,1,1-trichloroethane (2 mL) and vacuum-dried to thereby obtain a brownsolid (865 mg, yield: 53.2%). Melting point: 67.7 to 68.9° C.

¹H-NMR (CD₃CN): δ2.55 (s, 3H), 5.29 (q, J=8.2, 2H), 8.04 (dd, J=6.2,8.0, 1H), 8.50 (d, J=8.0, 1H), 8.62 (d, J=6.2, 1H), 8.64 (s, 1H)

¹⁹F-NMR (CD₃CN): δ−78.08 (s, 3F), −70.46 (t, J=8.2, 3F)

REFERENCE EXAMPLE 2

Synthesis of 1-(2,2,2-trifluoroethyl)-4-methylpyridiniumtrifluoromethanesulfonate

The procedure of Reference Example 1 was followed to synthesize thetitle compound from the corresponding starting compounds. Yield: 99%.Melting point: 100.0 to 101.0° C.

¹H-NMR (CD₃CN): δ2.68 (s, 3H), 5.29 (q, J=8.5, 2H), 7.96 (d, J=6.5, 2H),8.62 (d, J=6.5, 2H)

¹⁹F-NMR (CD₃CN): δ−78.11 (s, 3F), −70.80 (t, J=8.5, 3F)

REFERENCE EXAMPLE 3

Synthesis of 1-(2,2,3,3-tetrafluoropropyl)-2-methylpyridiniumtrifluoromethanesulfonate

The procedure of Reference Example 1 was followed to synthesize thetitle compound from the corresponding starting compounds. Yield: 99%.Melting point: 79.0 to 80.5° C.

¹H-NMR (acetone-d₆): δ3.09 (s, 3H), 5.71 (t, J=15.6, 2H), 6.76 (tt,J=52.2, 4.7, 1H), 8.18-9.19 (m, 4H)

¹⁹F-NMR (acetone-d₆): δ−137.71 (dt, J=4.3, 52.2, 2F), −120.80-−120.50(m, 2F), −78.25 (s, 3F).

REFERENCE EXAMPLE 4

Synthesis of 1-methyl-3-(2,2,2-trifluoroethyl)imidazoliumtrifluoromethanesulfonate

The procedure of Reference Example 1 was followed to synthesize thetitle compound from the corresponding starting compounds. Yield: 94%.Melting point: 51.0 to 51.9° C.

¹H-NMR (acetone-d₆): δ4.15 (s, 3H), 5.42 (q, J=8.6, 2H), 7.85-7.95 (m,2H), 9.34 (s, 1H)

19F-NMR (acetone-d₆): δ−79.18 (s, 3F), −71.53 (t, J=8.6, 3F)

REFERENCE EXAMPLE 5

Synthesis of 1-(2,2,2-trifluoroethyl)pyridiniumbis[(trifluoromethyl)sulfonyl]amide

1-(2,2,2-trifluoroethyl)pyridinium trifluoromethanesulfonate (4.8 mmol,1.50 g), synthesized from the corresponding starting compounds byfollowing the procedure of Reference Example 1, and LiN(SO₂CF₃)₂ (4.8mmol, 1.38 g) were heated in water (7.2 mL) at 70° C. for 4 hours. Thelayered reaction mixture was separated, and the reaction product waswashed with 1,1,1-trichloroethane (2 mL) and water (2 mL) andvacuum-dried to thereby obtain a white solid (1.87 g, yield: 88%).Melting point: 38.3 to 38.8° C.

¹H-NMR (acetone-d₆): δ5.93 (q, J=8.2, 2H), 8.43-9.50 (m, 5H)

¹⁹F-NMR (acetone-d₆): δ−78.97 (s, 6F), −70.91 (t, J=8.2, 3F)

REFERENCE EXAMPLE 6

Synthesis of 1-(2,2,2-trifluoroethyl)-4-methylpyridiniumbis[(trifluoromethyl)sulfonyl]amide

The procedure of Reference Example 5 was followed to synthesize thetitle compound from the corresponding starting compounds. Yield: 71.9%.Melting point: 60.3 to 61.1° C.

¹H-NMR (CD₃CN): δ2.71 (s, 3H), 5.27 (q, J=8.2, 2H), 7.98 (d, J=6.5, 2H),8.59 (d, J=6.5, 2H)

¹⁹F-NMR (CD₃CN): δ−78.95 (s, 6F), −70.79 (t, J=8.2, 3F)

B. Production of the Room-temperature Molten Salt of the PresentInvention

EXAMPLE 1

1-(2,2,2-trifluoroethyl)-3-methylpyridinium trifluoromethanesulfonate(30 mg) and 1-(2,2,2-trifluoroethyl)pyridiniumbis[(trifluoromethyl)sulfonyl]amide (30 mg) were fully mixed in a mortarin a dry atmosphere, to thereby obtain a product that was a colorlesstransparent liquid at room temperature.

EXAMPLE 2

1-(2,2,2-trifluoroethyl)-4-methylpyridinium trifluoromethanesulfonate(30 mg) and 1-(2,2,2-trifluoroethyl)pyridiniumbis[(trifluoromethyl)sulfonyl]amide (30 mg) were mixed in the samemanner as in Example 1, to thereby obtain a product that was a lightyellow transparent liquid at room temperature.

EXAMPLE 3

1-(2,2,3,3-tetrafluoropropyl)-2-methylpyridiniumtrifluoromethanesulfonate (30 mg) and 1-(2,2,2-trifluoroethyl)pyridiniumbis[(trifluoromethyl)sulfonyl]amide (30 mg) were mixed in the samemanner as in Example 1, to thereby obtain a product that was a colorlesstransparent liquid at room temperature.

EXAMPLE 4

1-methyl-3-(2,2,2-trifluoroethyl)imidazolium trifluoromethanesulfonate(30 mg) and 1-(2,2,2-trifluoroethyl)pyridiniumbis[(trifluoromethyl)sulfonyl]amide (30 mg) were mixed in the samemanner as in Example 1, to thereby obtain a product that was a lightyellow transparent liquid at room temperature.

EXAMPLE 5

1-(2,2,2-trifluoroethyl)-3-methylpyridinium trifluoromethanesulfonate(30 mg) and 1-(2,2,2-trifluoroethyl)-4-methylpyridiniumbis[(trifluoromethyl) sulfonyl]amide (30 mg) were fully mixed in thesame manner as in Example 1, to thereby obtain a product that was alight yellow transparent liquid at room temperature.

EXAMPLE 6

1-(2,2,3,3-tetrafluoropropyl)-2-methylpyridiniumtrifluoromethanesulfonate (30 mg) and1-(2,2,2-trifluoroethyl)-4-methylpyridinium bis[(trifluoromethyl)sulfonyl]amide (30 mg) were fully mixed in the same manner as in Example1, to thereby obtain a product that was a colorless transparent liquidat room temperature.

EXAMPLE 7

1-(2,2,2-trifluoroethyl)-3-methylpyridinium trifluoromethanesulfonate(30 mg), 1-(2,2,2-trifluoroethyl)pyridiniumbis[(trifluoromethyl)sulfonyl]amide (30 mg) and1-(2,2,2-trifluoroethyl)-4-methylpyridiniumbis[(trifluoromethyl)sulfonyl]amide (30 mg) were fully mixed in a mortarin a dry atmosphere, to thereby obtain a colorless transparent productthat was liquid at room temperature.

EXAMPLE 8

1-methyl-2-ethylpyridinium trifluoromethanesulfonate (30 mg) and1-(2,2,2-trifluoroethyl)pyridinium bis[(trifluoromethyl)sulfonyl]amide(30 mg) were mixed in the same manner as in Example 1, to thereby obtaina colorless transparent product that was liquid at room temperature.

The solidifying point of 1-methyl-2-ethylpyridiniumtrifluoromethanesulfonate measured by the method described in Experiment1 was −39° C.

EXAMPLE 9

1-methyl-2-ethylpyridinium trifluoromethanesulfonate (30 mg) and1-methyl-3-(2,2,2-trifluoroethyl)imidazoliumbis[(trifluoromethyl)sulfonyl]amide (30 mg) were mixed in the samemanner as in Example 1, to thereby obtain a colorless transparentproduct that was liquid at room temperature.

The solidifying point of 1-methyl-3-(2,2,2-trifluoroethyl)imidazoliumbis[(trifluoromethyl)sulfonyl]amide measured by the method described inExperiment 1 was −66° C.

Experiment 1 (Measurement of Solidifying Point)

The solidifying points of the room-temperature molten salts obtained inExamples 1 to 7 were measured by the following method: Eachroom-temperature molten salt was placed in an argon atmosphere in anairtight container and cooled at a rate of 2° C. to 3° C./min. Thetemperature at which the room-temperature molten salt began toprecipitate as a solid was determined as the solidifying point. Table 1shows the measurement results. TABLE 1 Solidifying point ofroom-temperature molten salt Solidifying Example point (° C.) 1 −87.0 2−60.0 3 −78.7 4 −85.0 5 −72.7 6 −72.8 7 <−90.0 8 <−90.0 9 <−90.0

Table 1 reveals that all the room-temperature molten salts had a verylow solidifying point.

COMPARATIVE EXAMPLE 1

1-(2,2,2-trifluoroethyl)-3-methylpyridinium trifluoromethanesulfonate(30 mg) and 1-(2,2,2-trifluoroethyl)-4-methylpyridiniumtrifluoromethanesulfonate (30 mg) were mixed in the same manner as inExample 1, but the resulting mixture remained solid at room temperature.

COMPARATIVE EXAMPLE 2

1-(2,2,2-trifluoroethyl)-2-methylpyridinium trifluoromethanesulfonate(30 mg) and l-(2,2,2-trifluoroethyl)-4-methylpyridiniumtrifluoromethanesulfonate (30 mg) were mixed in the same manner as inExample 1, but the resulting mixture remained solid at room temperature.

COMPARATIVE EXAMPLE 3

1-(2,2,2-trifluoroethyl)-4-methylpyridiniumbis[(trifluoromethyl)sulfonyl]amide (30 mg) and1-(2,2,2-trifluoroethyl)pyridinium bis[(trifluoromethyl)sulfonyl]amide(30 mg) were mixed in the same manner as in Example 1, but the resultingmixture remained solid at room temperature.

COMPARATIVE EXAMPLE 4

1-(2,2,2-trifluoroethyl)-4-methylpyridinium trifluoromethanesulfonate(30 mg) and 1-(2,2,2-trifluoroethyl)-4-methylpyridiniumbis[(trifluoromethyl) sulfonyl]amide (30 mg) were mixed in the samemanner as in Example 1, but the resulting mixture remained solid at roomtemperature.

As is apparent from the above, when two or more different organic saltswith the same anionic or cationic moiety are mixed, the solidifyingpoint lowers only slightly as compared with in the room-temperaturemolten salt of the present invention, and the resulting mixture is notliquid at room temperature. This matter is specifically demonstrated byComparative Examples 1, 2 and 3 in which two types of organic salts withthe same anionic moiety were mixed, and in Comparative Example 4 inwhich two types of organic salts with the same cationic moiety weremixed.

In contrast, when organic salts that were different not only in cationicmoiety but also in anionic moiety were mixed, the resulting mixture wasliquid and had a remarkably lowered solidifying point. Comparisonbetween Example 2 and Comparative Example 3 illustrates this point.

Experiment 2 (Differential Scanning Calorimeter (DSC) Measurement)

Differential scanning calorimeter (DSC) measurements were carried out onthe room-temperature molten salts of Examples 1, 3 and 4 and on1-ethyl-3-methylimidazolium trifluoromethanesulfonate, which is aroom-temperature molten salt obtained from Aldrich (Comparative Example5). A DSC-50 of Shimadzu Corp. was used for the measurements. Fivemilligrams of sample was weighed out, sealed in an aluminium cell, andplaced in the DSC chamber together with a reference (an empty aluminiumcell). While being purged with nitrogen at a rate of 20 ml/min, thechamber was cooled from room temperature to −120° C. at a rate of 1° C.to 5° C./min using liquid nitrogen. After being maintained at −120° C.for 30 minutes, the chamber temperature was raised to 100° C. at a rateof 10° C./min, and the data obtained during the temperature rise wascollected. FIGS. 1 to 4 shows the measurement results.

The figures reveal that the melting point (Tm) was observed around −13°C. in Comparative Example 5, whereas in Examples 1, 3 and 4, no meltingpoint (Tm) was observed and only the glass transition temperature (Tg)was observed around −60° C.

INDUSTRIAL APPLICABILITY

According to the present invention, at least two types of organic saltsthat are different from each other both in anionic moiety and cationicmoiety are mixed, with the result that the solidifying point isremarkably lowered and a liquid mixed organic salt (room-temperaturemolten salt) with a lower solidifying point is obtained.

Preferably, at least one, and more preferably all, of the organic saltsto be mixed are solids at room temperature. By mixing organic salts thatare solids at room temperature, the solidifying point is lowered,thereby giving a mixed organic salt that is liquid at room temperature(room-temperature molten salt). In this case, the starting organic saltsare all solids at room temperature, and can therefore be easily purifiedto a high purity by recrystallization or like processes. By mixing suchhigh-purity organic salts, the room-temperature molten salt of thepresent invention can be easily obtained in high purity.

The room-temperature molten salt of the present invention has aremarkably lower solidifying point and retains its liquid state over awider temperature range than single-component room-temperature moltensalts, and therefore shows promise for a wide variety of applications.Moreover, unlike single-component room-temperature molten salts, theroom-temperature molten salt of the present invention can be givenvarious properties suitable for various applications by appropriatelyselecting the types and proportions of the starting organic salts.

Due to the above features, the room-temperature molten salt of thepresent invention can be suitably used for nonaqueous batteryelectrolytes or electrolytic solutions, which are required to have highpurity. Further, the room-temperature molten salt of the presentinvention has a very low solidifying point, and thus can provide abattery with excellent low-temperature properties.

The room-temperature molten salt of the present invention can also beused as a solvent for various organic synthesis reactions and as anextraction solvent for separation and purification in organic synthesis.

Further, since the room-temperature molten salt of the present inventionhas high heat resistance, is liquid over a wide temperature range andhas high ionic conductivity, it can also be used as an electrolyticsolution for various plating processes.

The room-temperature molten salt of the present invention does notundergo a phase change until it reaches a low temperature and hasexcellent low temperature properties. Because of these features, theroom-temperature molten salt can be used as an electrolyte and/orelectrolytic solution for fuel cells, dye-sensitized solar cells,biological batteries or capacitors, an electro-rheological fluid, a heatstorage medium, a catalyst, etc.

1. A room-temperature molten salt comprising a mixture of two or moreorganic salts with different anionic moieties and different organiccationic moieties, the room-temperature molten salt having a solidifyingpoint lower than that of any of the individual organic salts.
 2. Aroom-temperature molten salt according to claim 1, wherein the two ormore organic salts are selected from the group consisting of the organicsalts represented by formulae (I), (II), (Im) and (IV):

wherein R^(1a) to R^(5a), R^(7a), R^(9a) and R^(10a) are the same ordifferent and each represents a hydrogen atom, a halogen atom, an alkylgroup, a cycloalkyl group, a heterocyclic group, a haloalkyl group, anaralkyl group, an aryl group, an alkoxy group, an aryloxy group or anaralkyloxy group; R^(8a) is a hydrogen atom, an alkyl group, acycloalkyl group, a heterocyclic group, a haloalkyl group, an aralkylgroup or an aryl group; R^(6a), R^(11a), R¹², R¹³, R¹⁴, R¹⁵, R¹⁶, R¹⁷,R¹⁸ and R¹⁹ are the same or different and each represents an alkylgroup, a cycloalkyl group, a heterocyclic group, a haloalkyl group, anaralkyl group or an aryl group; two groups selected from R¹², R¹³, R¹⁴and R¹⁵ may be linked at their ends to form, together with the adjacentnitrogen atom, a nitrogen-containing aliphatic heterocycle; two groupsselected from R¹⁶, R¹⁷, R¹⁸ and R¹⁹ may be linked at their ends to form,together with the adjacent phosphorus atom, aphosphorus-containingaliphatic heterocycle; and X₁ ⁻, X₂ ⁻, X₃ ⁻ and X₄ ⁻ are each aconjugate base of a Brönsted acid.
 3. A room-temperature molten saltaccording to claim 1 or 2, wherein at least one of the two or moreorganic salts is a solid at room temperature.
 4. A room-temperaturemolten salt according to claim 1 or 2, wherein all of the two or moreorganic salts are solids at room temperature.
 5. A room-temperaturemolten salt according to claim 1 or 2, wherein at least one of the twoor more organic salts is selected from the group consisting of theorganic salts represented by formulae (V) and (VI):

wherein R¹ to R⁵, R⁷, R⁹ and R¹⁰ are the same or different and eachrepresents a hydrogen atom, a halogen atom, an alkyl group, a cycloalkylgroup, a heterocyclic group, a haloalkyl group, an aralkyl group, anaryl group, an alkoxy group, an aryloxy group or an aralkyloxy group; R⁸is a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclicgroup, a haloalkyl group, an aralkyl group or an aryl group; R⁶ and R¹¹are the same or different and each represents a C₁₋₁₀ alkyl group inwhich at least one hydrogen atom is substituted by fluorine; and X₁ ⁻and X₂ ⁻ are each a conjugate base of a Brönsted acid.
 6. Aroom-temperature molten salt according to claim 5, wherein all of thetwo or more organic salts are selected from the group consisting of theorganic salts represented by formulae (V) and (VI).
 7. Aroom-temperature molten salt according to claim 5, wherein at least oneof the two or more organic salts is a solid at room temperature.
 8. Aroom-temperature molten salt according to claim 5, wherein all of thetwo or more organic salts are solids at room temperature.
 9. Aroom-temperature molten salt according to claim 5, wherein, in formulae(V) and (VI), R¹ to R⁵, R⁷, R⁹ and R¹⁰ are the same or different andeach represents a hydrogen atom, a halogen atom, an alkyl group or ahaloalkyl group; R⁸ is an alkyl group; R⁶ and R¹¹ are the same ordifferent and each represents a group of the formula —CH₂R¹² wherein R¹²is a straight- or branched-chain C, -alkyl group in which at least onehydrogen atom is substituted by fluorine.
 10. A room-temperature moltensalt according to claim 6, wherein all of the two or more organic saltsare selected from the group consisting of the organic salts representedby formula (V) and are solids at room temperature.
 11. Aroom-temperature molten salt according to claim 6, wherein all of thetwo or more organic salts are selected from the group consisting of theorganic salts represented by formula (VI) and are solids at roomtemperature.
 12. A room-temperature molten salt according to claim 6,wherein the two or more organic salts are at least one organic salt thatis selected from the group consisting of the organic salts representedby formula (V) and is a solid at room temperature, and at least oneorganic salt that is selected from the group consisting of the organicsalts represented by formula (VI) and is solid at room temperature. 13.A room-temperature molten salt according to claim 6, wherein the two ormore organic salts are two organic salts that are selected from thegroup consisting of the organic salts represented by formulae (V) and(VI) and that are solids at room temperature; one of the organic saltshaving an anionic moiety represented by the formula(RfSO₂)₂N⁻ or (RfSO₂)(Rf′SO₂)N⁻ wherein Rf and Rf′ are different andeach represents a polyfluoroalkyl group; and the other of the organicsalts having an anionic moiety represented by the formulaRf′SO₃ ⁻ wherein Rf′ is a polyfluoroalkyl group.
 14. A room-temperaturemolten salt obtainable by mixing two or more organic salts withdifferent anionic moieties and different organic cationic moieties, theroom-temperature molten salt having a solidifying point lower than thatof any of the individual organic salts.
 15. A process for producing aroom-temperature molten salt, comprising mixing two or more organicsalts with different anionic moieties and different organic cationicmoieties, the room-temperature molten salt having a solidifying pointlower than that of any of the individual organic salts.
 16. A processaccording to claim 15, wherein the two or more organic salts areselected from the group consisting of the organic salts represented byformulae (I) to (IV).
 17. A process according to claim 15 or 16, whereinat least one of the two or more organic salts is a solid at roomtemperature.
 18. A process according to claim 15 or 16, wherein all ofthe two or more organic salts are solids at room temperature.
 19. Aprocess according to claim 15, wherein the two or more organic salts areselected from the group consisting of the organic salts represented byformulae (V) and (VI) and are solids at room temperature.
 20. Anelectrolytic solution comprising a room-temperature molten saltaccording to claim 1 or claim
 14. 21. A battery comprising anelectrolytic solution according to claim 20, a positive electrode, anegative electrode and a separator.
 22. A battery according to claim 21,which is a nonaqueous lithium secondary battery.
 23. A solvent for usein organic reaction solvent comprising a room-temperature molten saltaccording to claim 1 or claim
 14. 24. An extraction solvent comprising aroom-temperature molten salt according to claim 1 or claim
 14. 25. Acapacitor comprising an electrolyte or electrolytic solution thatcomprises a room-temperature molten salt according to claim 1 or claim14.
 26. An electric double layer capacitor comprising an electrolyte orelectrolytic solution that comprises a room-temperature molten saltaccording to claim 1 or claim
 14. 27. A dye-sensitized solar cellcomprising a room-temperature molten salt according to claim 1 or claim14.
 28. A fuel cell comprising a room-temperature molten salt accordingto claim 1 or claim
 14. 29. A polymer electrolyte fuel cell comprising aroom-temperature molten salt according to claim 1 or claim 14.